The present invention relates to a rotary pump for liquid and more particularly to a rotary pump of the immersed rotor type with a bearing wear indicator.
The present invention is particularly applicable to a liquid rotary pump where the liquid immerses the motor rotor that is isolated from the motor stator by a shield, often referred to as a xe2x80x9ccanxe2x80x9d or xe2x80x9cjacket.xe2x80x9d This type of pump has been manufactured for many years and includes a shaft for rotatably mounting the rotor of the motor driving the pump. To center the rotor in the pump housing it has proven quite beneficial to use a mechanism having axially spaced conical bearings. Such a pump and bearings are disclosed in Young U.S. Pat. No. 3,195,466. Conical shaft bearings not only center the rotor and maintain the axial position of the pump impeller, but also provides the friction surfaces between the pump housing and the rotating elements within the pump. Young U.S. Pat. No. 3,195,466 is incorporated by reference as background information so that the details of the particular pump and bearings to which the present invention is directed need not be repeated by merely describing known pump technology. Through the years, patents have issued directed toward mechanical changes in the immersed rotor type of liquid pump. Two of these patents are Spisiak U.S. Pat. No. 3,225,698 and Neal U.S. Pat. No. 3,433,164. These patents are also incorporated by reference herein as background pump technology that need not be repeated in describing and understanding the present invention. The rotary pump to which the present invention is specifically directed is an improvement or modification of an existing pump sold by Buffalo Pumps of North Tonawanda, N.Y. The interior design of the preferred embodiment is the same as the pumps marketed by Buffalo Pumps for some years. This well known design is disclosed in Buffalo Pumps Bulletins 929A and 985, which bulletins are incorporated by reference herein to show how the pump to which the present invention is directed employs the patented background technology. These bulletins also disclose the fluid thrust balancing mechanism used in some of the immersed rotor pumps, but this feature does not constitute a feature of the present invention. All of this background material shows use of axially spaced conical bearings for supporting the immersed rotor of a rotary pump.
The present invention relates to a wear detector using a vibration member for activation when wear of the conical bearings reaches a certain limit. A wear detector is shown in Vaughn U.S. Pat. No. 5,944,489; however, it relates to another sensing mechanism and is not associated with conical bearings. Sensing of bearing vibration is disclosed in Meyer U.S. Pat. No. 4,237,454. This patent relates to the actual vibration caused by the defective bearing and not a mechanism to cause vibration. These two patents are incorporated by reference herein.
The present invention involves a mechanism causing the housing of a pump to violently vibrate when there is excessive bearing wear. This vibration is detected by a device involving a model 162 VTRA vibration transmitter on the housing. The transmitter is connected to a series 440 vibration switch. The lights on the transmitter indicate when the vibration device has been triggered by rotation of the internal wear detector. Incorporated by reference herein are specification sheets for the vibration transmitter (162 VTRA) and the vibration switch (440) contemplated for use in practicing the present invention.
The immersed rotor type rotary pump which has proven to be the most successful through the years includes axially spaced conical bearings. These conical bearings each have a journal element that is self lubricating carbon graphite with an internal taper and mounted for radial movement in the pump housing. The internal taper or conical bearing surface of the journal or second element of the bearing matches the tapered or conical bearing surface of a first element formed as part of the shaft of the immersed motor rotor. In this type pump stainless steel coil springs in the journal recess of the pump housing forces the axially movable bearing elements or journals toward the fixed matching elements on the rotor shaft. Thus, from both ends of the rotor, a coil spring biases the two journal elements of the spaced conical bearings into engagement with the shaft elements to provide a bearing force that maintains the radial position of the rotating rotor. In addition, the conical bearings have a force component that maintains the axial position of the rotor within the pump housing. Consequently, the conical bearings which have been used for decades are quite successful and constitute an inexpensive mechanism to maintain self-centering of the rotor for control of both the radial and axial positions of the rotating components of the pump. During bearing wear, the matching conical bearing surfaces maintain the radial position of the rotating components of the pump. In addition, one beneficial feature of using conical bearings is that the bearings have a self-centering ability in an axial direction based upon the liquid pressure around the rotor. The thrust balancing feature uses a pressure differential between the front of the rotor and the back of the rotor so that the hydraulic forces move the conical bearings slightly to center the rotor. This balancing is accomplished by spring biased conical bearings.
The conical bearings that are spring biased have an initial axial position after thrust balance, which position should be maintained over long term use of the pump. When the conical bearings have reached approximately xe2x85x9 inch of wear, it is desirable to replace or repair the journals of the pump bearings to maintain trouble free operation. Wear of the conical bearings is normally discovered during regular inspection involving disassembly of the pump. However, it is desirable to know when bearing wear reaches a given amount for the purposes of tending to proper preventive maintenance. At this time, rotary pumps of the immersed rotor type are subject to periodic maintenance or inspection. The time between such inspections must be quite short to assure maintenance is performed before the pump fails due to excessive bearing wear. Catastrophic bearing failure must be avoided. Bearing wear can be accelerated by the type of fluid being pumped or by contaminants in the pumped liquid. Consequently, it is preferred practice to inspect the conical bearings long before they need to be refurbished to assure long term operation of the pump. These factors make maintenance of conical bearings a relatively expensive and time consuming activity.
The present invention relates to the concept of detecting wear of the conical bearings to determine when they should be replaced and/or refurbished. Consequently, frequent inspection of the bearings is not necessary. Bearings are given attention only when actually needed. This is a substantial advantage, is cost effective and prevents catastrophic failure based upon bearing malfunction. In the past, such failure could occur between even short term inspections. The invention involves an improvement in a rotary pump of the type described and incorporated by reference herein. Real time monitoring of the conical bearing wear is the result of using the invention. An excessive wear detecting device uses an imbalance member that is associated with each of the axially spaced conical bearings. The imbalance ring or plate (i.e. member) surrounds the shaft and includes a drive member axially spaced outwardly from a drive member on the rotating shaft. As the bearing being monitored is subject to wear, the two drive members move together and ultimately engage. This causes the shaft to rotate the imbalance member to drastically increase the vibration of the pump housing. A sensor detects the drastic increase in the housing vibration to indicate bearing wear at a monitored amount. During operation of the pump the conical bearings and the rotor assembly move axially to maintain the hydraulic thrust balance as previously described. This balanced axial position allows the housing to carry the imbalance member without rotation by the shaft. As the conical bearings wear, the drive members on the imbalance element and the shaft move axially toward each other. When there is a given amount of wear, the imbalance member carried by the bearing element on the housing is engaged by the shaft drive element and starts to rotate. In this manner, the present invention provides a mechanical event indicating when bearing wear is at a given amount. The change in spacing bearing journals is indicative of a need to replace the bearings or otherwise attend to the bearings in the pump. The wear detecting device of the present invention is easily installed on existing canned pump designs. There is no need to modify the pump pressure boundary to disturb the integrity of zero leakage designs. A wear detector imbalance member is merely assembled in the housing of the pump adjacent each of the conical bearings and an engaging element is fixed on the shaft. The wear characteristics of the bearings are monitored by action of these two components.
In accordance with the present invention, there is provided a rotary pump for liquid. The pump has a housing, a shaft carrying a motor rotor, a motor stator fixed in the housing and surrounding the rotor to rotate the rotor and shaft about an axis. The shaft is mounted in the housing by axially spaced conical bearings, each bearing includes a first element fixed on the shaft with a first conical bearing surface concentric with the rotational axis, a coacting second element carried by the housing with a second conical bearing surface centered with the axis and slidably engaging the first bearing surface and a spring forcing the two elements together to center the rotor with respect to the stator. The invention involves a wear indicator comprising a cage attached to and movable axially with the second element of one of the bearings as the bearing surfaces wear. This cage surrounds the shaft and carries an imbalance plate or ring with an outer portion supported on the cage for free rotation in the cage and an inner portion surrounding, but normally spaced from the shaft. There is a first drive member fixed on the shaft and a second drive member on the plate or ring and axially aligned with the first drive member so the members engage each other when the cage moves axially a given distance whereby the imbalance plate or ring is rotated in the cage by the shaft. Rotation of this imbalance plate or ring causes drastic vibration, which vibration is sensed on the motor housing to indicate wear of a given amount by the internal conical bearing or bearings. In accordance with another aspect of the invention, a given distance of wear is xc2xc-xe2x85x9 inch, and preferably about xe2x85x9 inch. The first drive member is a tapered nose on a sleeve mounted to rotate with the shaft. The second drive member is a tapered opening in the imbalance plate or ring that surrounds the tapered nose. As these two members move together upon bearing wear, they ultimately engage. The two tapered surfaces rotate the imbalance member, plate or ring to cause drastic vibration of the pump housing. This vibration is sensed to indicate undue wear of at least one of the bearings. In accordance with an aspect of the invention, the imbalance plate, ring or member is a wheel like element with a substantially different mass at one circumferentially spaced areas. Rotation of this member causes drastic vibration. In accordance with an aspect of the invention, the cage is forced against the second element by the spring.
The primary object of the present invention is the provision of a rotary liquid pump of the type having spaced conical bearings, which pump is provided with a wear indicator of the type having an imbalance element or member engaged and rotated by the shaft for signaling excessive bearing wear.
Still a further object of the present invention is the provision of a rotary pump as defined above, which pump incorporates a commercial vibration detector mounted on the housing. When this detector senses unusually violent vibrations, a signal is provided to indicate bearing wear.
Yet another object of the present invention is the provision of a rotary pump, as defined above, which pump is the sealed stator type and includes the wear indicator that is easily mounted on existing immersed rotor rotary pumps.